Compensation Liquid for a Compressed Gas Energy Storage System

Abstract

A hydrostatically compensated, compressed gas energy storage system can include an accumulator containing a layer of compressed gas at between about 20 bar and about 90 bar above a layer of compensation liquid that has a density of at least 1500 kg/m3. A compressor and expander subsystem may be configured to selectably convey compressed gas into the accumulator and to extract gas from the accumulator. The system may be operable in at least a charging mode in which the compressor and expander subsystem conveys gas into the layer of compressed gas thereby displacing a corresponding volume of compensation liquid from the layer of compensation liquid within the accumulator out of the accumulator via the compensation liquid flow path thereby maintaining the layer of compressed gas at substantially the accumulator pressure during the charging mode.

1 . A hydrostatically compensated, compressed gas energy storage system comprising:
 a) an accumulator disposed underground and comprising an interior for containing a layer of compressed gas above a layer of compensation liquid, the layer of compressed gas being at an accumulator pressure that is between about 20 bar and about 90 bar and the compensation liquid having a density of at least 1500 kg/m 3 ;   b) a compressor and expander subsystem in fluid communication with the accumulator interior via a gas flow path and configured to selectably convey compressed gas into the accumulator and to extract gas from the accumulator;   c) a compensation liquid reservoir spaced apart from the accumulator and a compensation liquid flow path extending between the compensation liquid reservoir and the layer of compensation liquid within the accumulator; and   the system being operable in at least a charging mode in which the compressor and expander subsystem conveys gas into the layer of compressed gas thereby displacing a corresponding volume of compensation liquid from the layer of compensation liquid within the accumulator out of the accumulator via the compensation liquid flow path thereby maintaining the layer of compressed gas at substantially the accumulator pressure during the charging mode.   
     
     
         2 . The system of  claim 1 , wherein the system is operable in a discharging mode in which the compressor and expander subsystem extracts gas from the layer of compressed gas as a corresponding volume of compensation liquid flows from compensation liquid flow path into the layer of compensation liquid within the accumulator thereby maintaining the layer of compressed gas at substantially the accumulator pressure during the discharging mode. 
     
     
         3 . The system of  claim 1 , wherein the compensation liquid is a slurry comprising solid particles suspended in water. 
     
     
         4 . The system of  claim 3 , wherein the solid particles comprise particles formed from at least one of clay, ore, sand, rocks, magnetite, limestone, iron ore, copper concentrate. 
     
     
         5 . The system of  claim 4 , wherein the solid particles comprise one of magnetite, limestone, iron ore, and copper concentrate. 
     
     
         6 . The system of  claim 3 , wherein at least 90% of the solid particles remain in suspension in the water for at least 12 hours. 
     
     
         7 . The system of  claim 6 , wherein at least 90% of the solid particles remain in suspension in the water for at least 48 hours. 
     
     
         8 . The system of  claim 6 , wherein at least 90% of the solid particles remain in suspension in the water for at least 1 week. 
     
     
         9 . The system of  claim 1 , wherein the compensation liquid density is less than 2400 kg/m3. 
     
     
         10 . The system of  claim 1 , further comprising an agitating system configured to agitate the compensation liquid within the compensation liquid reservoir to help keep solid particles suspended in water. 
     
     
         11 . The system of  claim 1 , wherein the accumulator pressure is at least 50 bar. 
     
     
         12 . The system of  claim 1 , wherein the accumulator is disposed at an accumulator depth that is between about 200 m and about 700 m. 
     
     
         13 . The system of  claim 12 , wherein the accumulator depth is less than 500 m. 
     
     
         14 . The system of  claim 1 , wherein:
 a) the compensation liquid flow path comprises a shaft having a lower end adjacent the accumulator, an upper end spaced apart from the lower end, and a shaft sidewall extending upwardly from the lower end to the upper end and at least partially bounding a shaft interior containing a quantity of the compensation liquid, the shaft interior being fluidly connected to the compensation liquid reservoir; and   b) further comprising a partition separating an interior of the accumulator from the shaft interior, the partition having an outer surface in contact with the quantity of compensation liquid within the shaft interior and an opposing inner surface in contact with the layer of compressed gas and the layer of compensation liquid,   whereby at least one of the layer of compressed gas and the layer of compensation liquid bears against and exerts an internal accumulator force on the inner surface of the partition and the quantity of liquid within the shaft bears against and exerts an external hydrostatic counter force on the outer surface of the partition, so that a partition force acting on the partition while the compressed gas energy storage system is in use is a difference between the accumulator force and the hydrostatic counter force and is less than the accumulator force.   
     
     
         15 . The system of  claim 14 , wherein the shaft interior is fluidly connected to the layer of compensation liquid by a liquid supply conduit so that the compensation liquid can flow between the shaft interior and the layer of liquid in the accumulator in response to changes in the pressure of the layer of compressed gas. 
     
     
         16 . The system of  claim 15 , wherein the liquid supply conduit passes thorough the partition or beneath the partition. 
     
     
         17 . The system of  claim 14 , wherein a liquid supply conduit extends between a first end that is proximate the outer surface of the partition and is in fluid communication with the shaft and a second end that is in communication with the layer of compensation liquid and remains fluidly isolated from the layer of gas when the compressed gas energy storage system is in use. 
     
     
         18 . The system of  claim 1 , wherein the gas flow path comprises a gas supply conduit configured to convey compressed gas between the layer of compressed gas and the compressor and expander subsystem, and wherein at least a portion of an outer surface of the gas supply conduit is in contact with the compensation liquid in the compensation liquid flow path. 
     
     
         19 . The system of  claim 18 , wherein the gas supply conduit passes through a partition. 
     
     
         20 . The system of  claim 1 , wherein the gas flow path comprises a gas supply conduit that is external to the liquid flow path and is configured to convey compressed gas between the layer of compressed gas and the compressor and expander subsystem.